There are increasing demands for compact, high-power dynamoelectric machines, both motors and generators, and particularly generators for mobile applications. Superconducting generators become competitive with conventional generators as power demands increase.
Superconducting dynamoelectric machines typically require rotors that comprise high temperature superconductors. Such rotor superconductors require an operating temperature near 30 K for the typical combination of electric current density and magnetic flux density that they support. The most accepted approach for cooling such dynamoelectric machine rotors comprises circulating cold, gaseous helium from an external cryogenic cooler into the rotor. Although this approach may be satisfactory for stationary dynamoelectric machines that operate at relatively low rotational speeds, the use of conventional large external cryogenic coolers for compact mobile applications, and particularly aeronautical applications, are not satisfactory from the standpoint of weight alone. In addition, high-performance, low-temperature rotating seals are required for the entry and exit of helium ports in the dynamoelectric machine shaft. These types of seals are not likely to withstand ordinary dynamoelectric machine service life in aeronautical applications wherein rotational speeds may be near 15,000 rpm.